A protester who threw one of his shoes at the Chinese premier, Wen Jiabao, during a lecture at Cambridge University behaved "unreasonably" and could have caused serious injury, a court heard today.

Martin Jahnke, 27, a German studying pathology at Darwin College, Cambridge, called Wen a "dictator" and accused senior Cambridge University staff of "prostituting themselves" by allowing him to speak, a district judge sitting in Cambridge was told. Jahnke threw the shoe towards the stage where Wen was standing and it landed a few metres from the Chinese leader, Cambridge magistrates court heard.

The student is accused of using words and behaviour likely to cause harassment, alarm or distress to Wen or others. He denies any offence.

The judge, Ken Sheraton, was told the incident happened on 2 February while the premier was on a state visit.

Caroline Allison, prosecuting, said Jahnke disturbed Wen's Cambridge speech by whistling. "He was heard shouting words to the effect that the university was prostituting themselves by allowing the premier to speak and referred to the premier as a dictator," she said.

"He picked up one of his shoes, a trainer, which he then threw, which must have been with some force, on to the stage area a few yards away from where the premier was standing."

Allison added: "Mr Jahnke's behaviour in shouting and blowing a whistle may have started off as lawful protest but when he threw his shoe it became unreasonable behaviour and an act of aggression."

A police officer assigned to guard Wen told the court: "If the shoe had struck the premier in the face it could have caused serious injury to his eye or to his nose."

Allison said the shoe remained "unaccounted for". No statement on behalf of Wen, who was not present in court, was read out.

Three Chinese students at the lecture gave evidence for the prosecution. One said Jahnke seemed "excited and a little bit angry and threatening", adding that his behaviour made him feel "uneasy". Another said members of the audience seemed "shocked and frightened".

Jahnke's lawyers failed in an attempt to halt the trial on the grounds that prosecutors had been unduly influenced by the Chinese government. Tom Wainwright, for Jahnke, suggested politicians such as John Prescott and Peter Mandelson had been subjected to similar attacks by protesters in recent years but the protesters in those cases had not been charged.

Punam Malhan, the CPS lawyer who reviewed the case, said officers should have referred it to the CPS before making any decision on charging Jahnke. But she denied suggestions that the Chinese government had influenced the decision to prosecute.

"The police charged the defendant without reference to the CPS," she said. "It should have been referred to the CPS prior to charge." She said she could not explain why the police had charged without referring the case but said she had approved the prosecution.